Radiation therapy or “radiotherapy” can be used to treat cancers or other ailments. Generally, ionizing radiation in the form of a collimated beam is directed from an external source toward a patient. The dose of an applied radiation therapy beam or a sequence of applied radiation therapy beams is generally controlled such that a target locus within the patient, such as a tumor, receives a prescribed cumulative dose of radiation, while radiation-induced damage to healthy tissue surrounding the target locus is to be avoided. The radiation therapy beam can include high-energy photons, electrons, or other particles such as protons.
In one approach, a radiation therapy beam can be generated, for example, at least in part using a linear accelerator. The linear accelerator accelerates electrons and directs the electrons to a target, such as a metallic target, to elicit high-energy photons. The high-energy photons, generally having an energy in a mega-electron-volt (MeV) range for therapeutic use, can then be controlled, shaped, or modulated and directed to the target locus, such as a tumor region within the patient. A specified or selectable therapy beam energy can be used, such as for delivering a diagnostic energy level range or a therapeutic energy level range. Modulation of a therapy beam can be provided by one or more attenuators or collimators. The field size and shape of the radiation beam can be adjusted to avoid damaging healthy tissue adjacent to the targeted tissue by conforming the projected beam to a profile of the targeted tissue.
In one approach, a treatment plan can be developed before radiation therapy is delivered, such as using one or more medical imaging techniques. In such an approach, imaging can be performed in an “offline” manner. A health care provider, such as a physician, may use three-dimensional imaging information indicative of the patient anatomy to identify a target locus along with other regions such as organs near the tumor. Such imaging information can be obtained using various imaging modalities, such as X-ray, computed tomography (CT), magnetic resonance imaging (MRI), positron emission tomography (PET), or single-photon emission computed tomography (SPECT), etc. The health care provider can delineate the target locus that is to receive a prescribed radiation dose using a manual technique, and the health care provider can similarly delineate nearby tissue, such as organs, at risk of damage from the radiation treatment. Alternatively or additionally, an automated tool can be used to assist in identifying or delineating the target locus. A radiation therapy treatment plan can then be created based on clinical or dosimetric objectives, and constraints. The treatment plan can then be executed by positioning the patient and delivering the prescribed radiation therapy to the patient. The therapy treatment plan can include dose “fractioning,” whereby a sequence of radiation therapy deliveries are provided, with each therapy delivery including a specified fraction of a total prescribed dose.
As discussed above, a radiation therapy can be guided by images that provide knowledge of the target locus. However, certain anatomical regions, e.g., the lungs, are subject to quasiperiodic motion such as respiratory motion, that is significant enough to affect the treatment. For example, respiratory motion may change the locations of some organs, such as thoracic or abdominal organs. The movement of the organ caused by the respiratory motion can lead to imaging artifacts, making the images less effective in guiding the therapy. Therefore, further knowledge of the respiratory motion may be needed to plan an effective radiation therapy. However, unlike periodic motion, quasiperiodic motion does not have a fixed frequency, making it harder to predict future motions.
Moreover, the respiratory motion typically occurs for a relatively short time period. However, the process of taking an image, analyzing it, and determining the position of the target, can take a long time. That results in a latency between acquiring the mage and compensating for the respiratory motion. Therefore, the prediction of the respiratory motion is needed to allow a prediction of the target position in real time.
The disclosed methods and systems are designed to further improve the motion prediction.